tuning system



Dec. 23, 1952 G. w. WALLIN TUNING SYSTEM Original Filed Aug. 15, 1947 2SHEETS-SHEET 1 Hit N llll a IT- I I l h 1| INVENTOR. 6M5" m G. W. WALLINDec. 23, 1952 TUNING SYSTEM 2 SHEETS--SHEET 1 Original Filed Aug, 13,1947 AUDIO DISCR AMP Reissued Dec. 23, 1952 UNITED STATES PATENT OFFICETUNING SYSTEM Gus W. Wallin, Chicago, 111., assignor to Motorola,

Inc., Chicago, 111., a corporation of Illinois ated February 7, 1950,Se-

Original No. 2,496,322, 6

768,382, August 13, 1947. Application 29, 1950, Serial rial No. forreissue May 28 Claims.

Matter enclosed in heavy brackets II appears in reissue specification;matter printed in italics indicates the additions This invention relatesgenerally to tunable resonant systems and more particularly to atransmission line tuning system adapted for use in very high frequencysystems such as presently used for frequency modulation and televisionreceivers.

In the design of radio receivers for operation in the very highfrequency band such as the 88 to 108 megacycles band now assigned forfrequency modulation receivers, various difliculties are involved whichare not present in the design of receivers in the lower frequency bandsas used for standard amplitude modulation broadcast reception. Many ofthese problems relate to tuner design, and present condenser anpermeability tuners have not been satisfactory. In dealing with suchhigh frequencies, even when the tuning inductance is made as small aspracticable, the capacity required for tuning is relatively small.Accordingly, any changes in the inductance or capacity of tubes or othercomponents due to manufacturing tolerances and also changes While inuse, such as that caused by heating, have a very substantial effect.These changes in inductance and capacity cause the frequencies to driftand in particular produce instability in the oscillator circuit. Thisfrequency drift is particularly important in push button receiverswherein the desired channels are pre-set and merely selected by theoperator of the receiver. As push button tuning has become very popularand is considered almost essential in present day receivers, a tuningsystem adaptable to push button operation is highly desirable.

Further, in the very high frequency band, difficulty is encountered inobtaining the desired selectivity, that is, rejection of adjacentstations. This is due to the fact that to provide conventional tuningelements having the values required at this frequency the resultingcircuit has a very low Q. fhe low Q of such circuits also limits thestable gain that can be obtained therefrom.

It is, therefore, an object of the present invention to provide animproved tuner for use in the very high frequency range.

It is a further object of the present invention to provide a tuningsystem for use in the very high frequency range which providessufficient stability to permit push button operation.

the original patent but forms no part of this made by reissue.

Another object of the present invention is to provide a tunable resonantcircuit for use in the very high frequency range in which the effectiveQ of the circuit is very high providing good selectivity and permittinghigh gain.

It is a still further object of the present invention to provide atuning unit for use in very high frequency receivers in which the tuningcomponents are provided in a single relatively inexpensive unit.

A feature of this invention is the provision of a tuning unit includinga pair of series connected coaxial conductors with a movable iron corefor varying the permeability thereof and a concentric capacitor havingplates connected to said conductors.

Another feature of this invention is the provision of a tuning unit foruse with very high frequencies including a variable inductance and atuning condenser made as an integral unit so that the effect of theinductance of leads is substantially reduced.

A further feature of this invention is the provision of a resonantcircuit including a transmission line tuning unit having spacedconductors and an integral capacitor including plates connected to saidconductors in which said plates are movable with respect to each otherto provied initial tuning of the resonant circuit.

Still another feature of the present invention is the provision of aresonant circuit including a tuning unit with a tunable coaxialtransmission line and a plurality of capacitors including plates some ofwhich are secured to the conductors of the transmission line to providea pair of capacitors connected in series across the transmission lineproviding a center tap conneetion thereto.

A still further feature of this invention is the provision of a tunerfor tuning a plurality of circuits so that the resonant frequencies ofthe circuits have a predetermined relation throughout a band offrequencies, including tuning units in each circuit having integralinductors and capacitors, with the capacitors being variable to providethe desired frequency relation at one set of frequencies and theinductors being constructed to tune said circuits through said band offrequencies while sub-stantially maintaining said frequency relation.

Further objects, features and advantages will be apparent from thefollowing description taken in connection with the accompanying drawingsin which:

Fig. 1 is a perspective view showng the tuner accordance with theinvention;

Fig. 2 is a front view of the tuner of Fig. 1; Fig. 3 is across-sectional view of one section of the tuneralong. the lines 33 ofFig 2;

Fig. 4 is a fragmentary view of a portion of a tuner element along thelines 4-4 of Fig. 2;

Fig. 5 is a circuit diagram illustrating the use of the tuner inaccordance with the invention; and 1 Fig. 6 illustrates a modificationtuning element in accordance with the invention.

In practicing the invention there is provided a tuner including aplurality oftuning. units comprising a short section of a transmissionline including a center conductor and a coaXialouter conductor. Theconductors are connected together at one end so that they are in eifectconnected in series and the inductance thereof is varied by use of aferromagnetic core which is movable within the space between theconductors. Concentric capacitors are providedv at the open ends of theconductors having plates some of which are connected to the conductorsso that the capacitors are connected in parallel across the conductors.Arrangements are provided in which one: of the plates is movable withrespect to. another plate to provide a trimmer capacitor for useinaligning. the circuit being tuned. An arrangement isalso providedwherein a pair of condensers are connected in series across theconductorsto provide a center tap for the resonant circuit providedthereby. The tuning, units can be, arranged to. have different frequencycharacteristics. so thata plurality of units can be ganged to tune a.plurality of circuits in such a manner that a desired frequency relationis established: in the circuits throughout a band of frequencies.

Referring now to the drawings there is illustrated in. Figs. L and. 2 atuner III in accordance with..theinvention including three tuning unitsI I. The individual tuning units include a tunable transmission line andone or more capacitors- The tunable transmission line is disclosedandclaimedin my copending application Serial No. 625,145, filed October29, 1945. For varying the inductance of the coaxial transmission lines,ferromagnetic cores I2 movable in the space be tween the conductors. ofthe transmission lines areprovided. The core may also have some effecton the distributed capacity of the transmission line as the: binder usedmay have a dielectric constant greater than unity, but this efiect isnot substantial in the present application and the transmission linewill be considered as a variable inductance. In Fig. 1 a plurality ofcores I2 associatedwith the tuning units II are connected to a commoncarriage I3 for movement in unison to simultaneously tune a plurality ofcircuits as will befully described. For moving the carriage I3 a rackand pinion. mechanism is provided including a rack I4 which is a part ofthe carriage I3 and apinion I 5which is mounted on the chassis- I B. Thecarriage I3 slides on rods I l supported on the frame 23, therodslimiting the carriage to a linear up and downmovement, As

isapparent in- Fig. 2. aspring biased ball I8 bears against a portionIil of the frame to hold the carriage in a predetermined position. Thetuner is mounted on the chassis. I6 in an opening in the--chassis sothat the ends of the tuningunits theaouterconductor3| An additionalcapacitor is also II extend through the opening and connections can bemade thereto from the bottom of the chassis.

In Fig. 3 there is illustrated a cross-sectional view of one of thetuning units in accordance with the invention showing the details of theunit. In this figure the center conductor is indicated by 3,0. and theouter conductor by reference numeral'3 I. As is apparent, the innerconductor 30 has a portion 32 which is bent over and electricallyconnected to the outer conductor 3I. The movable ferromagnetic core I2includes a slot 33 therein which permits the core to be moved into thespace between the center conductor 30 and Insulation 38 is providedbetweenthe core I 2*and the cylindrical conductor 3I. This maybea sleevesecured to the conduct0113l as illustrated or may be a coating on eitherthe conductor 3| or the core I2. As previously stated, the core I2 ismoved by a carriage l3 and is preferably adjustably connected thereto.The connection between the'core and, carriage is illustrated asincluding abo-lt 34 secured to the core I 2 and a nut secured to thecarriage I3 by clip 35. This permits relative adjustment of the positionof the core with respect to the carriage I3. The outerconductor 3| ofthe tuning unit is secured between two insulating members 31 which aresupported by the frame structure 23 of the tuner.

To provide a capacity for tuning the trans-; mission line,v a pluralityof concentric capacitors may be connected directly to the transmissionline andconstructed as an integral part of the tuning unit. Fig. 3illustrates such a capacitor including a plate 40 which is connected tothe center conductor 39 anda plate 4I which is electrically connected toand supported by an annular cupshaped member 42 connected to the outerconductor 3I. A suitable dielectric material 43 is provided between theplates 40 and M which may be mica. As the plates 40 and M are connectedrespectively to the conductors 30 and 3|, the capacitor is'bridgedacross the transmission line. provided bridged across the transmissionline. the cup-shaped member 42 and the movable plate 44 forming theplates of this condenser. For permitting adjustment' of this capacitor,the plate 44 has a, threaded projecting portion 45 which engages threadson a ring 46 secured to the center conductor 30. This permits the plate44 to be moved with respect to the member 42 to provide a trimmercondenser across the transmission line. Insulating material 47 isprovided between the plates 42. and 44 to prevent shorting of thetransmission line when the trimmer condenser isbeing adjusted.Connections are made to the tuning unit including the transmission lineand the capacitors by lead 2 I. connected to the center conductor 30 andlead 22 connected to the outer conductor 3I. As the transmission lineand capacitors which form the tuned'circuit are directly connected as aunit, the effect of the inductance of the leads which is substantialat'very high frequencies is reduced.

Fig. 4 illustrates a different capacitor structure which may be combinedwith the transmission line to provide a tuning unit with a centerconnection to. the resonant circuit as required in a Colpittsoscillator. In. Fig. 4 the. conductors 30 and 3-I of the transmissionline and the core I2 may be of identical. construction to. that of Fig.3. A plurality of capacitors are provided by a plurality of annularconcentric conducting members designated 50, 51., 52 and 53; It. isnoted that these various members are separated by a plurality of discs54 made of suitable dielectric material such as mica. The member 50 issupported on and connected to the outer conductor 3i and the members 5|and 53 are both connected to the inner conductor 30. It is apparent thatthe members 50 and 5| provide a fixed capacitor bridged across thetransmission line. The members 50, 52 and 53 form a pair of capacitorsin series which are also bridged across the transmission line. That is,one capacitor is formed between member 50 connected to the outerconductor and member 52 whch is isolated from both conductors and asecond capacitor is formed between member 52 and members 5| and 53 whichare connected to the center conductor. Member 52, therefore, forms acenter tap in the resonant circuit as is required in certainapplications. The dielectric discs 54 separate the conducting members tocomplete the capacitor structures.

Fig. 5 illustrates the use of a tuner in accordance with the inventionin a very high frequency radio receiver. The circuit illustrated is ofthe double superheterodyne type in which a single oscillator is used forboth converters. Referring specifically to Fig. 5, the terminal 60 isadapted to be connected to an antenna. Tuning units 5!,

l0 and I4 tune the antenna, oscillator and variable intermediatefrequency, respectively. An electron discharge valve 62 is providedwhich includes two triode sections 63 and 64, the section 63 functioningas a combined oscillator and first converter, and the section 64 servingas a second converter. The antenna is connected to tuning unit 6| whichmay be of the construction illustrated in Fig. 3 and the signal selectedis applied to the grid 65 of the triode section 63, the grid bein biasedby resistor 65. Operating potential is applied to the plate 51 of thetriode 63 from +B voltage source through resistor 58. The cathode 69 isgrounded and connected to the center tap of the local oscillator circuitprovided by tuni'ng unit which is of the construction shown in Fig. 4. Aseparate trimmer capacitor H is required for aligning the oscillatorcircuit as a trimmer is not provided as an integral part of this tunngunit. The output of the first converter is a variable intermediatefrequency which is tuned by the unit M, being coupled thereto bycapacitor 12. This signal is applied through capacitor 13 to the grid ofthe second converter section 64 where the intermediate frequency isagain beat with the oscillator frequency to provide a fixed intermediatefrequency. The output of the second converter is applied from the platel! to inductively coupled coils 80 and Bi which are tuned by condensers82 and 83 to the second fixed intermediate frequency. The coil BI iscoupled to an intermediate frequency amplifier 84 which may be ofstandard construction wherein the signals are amplified and then appliedto discriminator 85. Amplitude modulation signals are derived in thediscriminator and applied to audio amplifier 85 wherein they areamplified and applied to a sound reproducing device 81.

In systems actually constructed adapted for use in the frequencymodulation bandof from 88 to 1 08 megacycles utilizing the circuit ofFig. 5, a fixed second intermediate frequency of 4.3 megacycles has beenused. In such a system the tuning unit BI is, of course, adapted to betuned to the signal frequency and the oscillator tuning unit 10 tuned toa frequency which is half the difference between the signal frequencyand intermediate frequency (4.3 megacycles). The

variable intermediate frequency differs from the oscillator frequency bythe fixed intermediate frequency (4.3 megacycles) and the tuning unit 14is arranged to be resonant at this frequency. Considering a megacyclesignal frequency, the oscillator frequency is 47.85 megacycles and thevariable intermediate frequency is 52.15 megacycles. When this variableintermediate frequency is heat with the 47.85 megacycles oscillator inthe second converter, the fixed intermediate frequency of 4.3 megacyclesis produced as de sired.

The physical characteristics of the transmission line are governed bythe electrical characteristics desired. As previously stated, the linesare used essentially as variable inductances, the value of theinductances depending upon the length of the lines. The anti-resonantimpedance of the line depends upon the ratio of diameter of the outerconductor to that of the inner conductor, a ratio of 9.2 to 1 havingbeen found to provide maximum impedance. To provide a plurality oftuning units for tuning a plurality of circuits having a predeterminedfrequency relation between the circuits, the various transmission linescan be produced in different lengths to thereby provide the inductanceranges required by the circuits. For tuning a circuit through afrequency range from 88 to 108 megacycles a transmission line having anouter conductor approximately .8 of an inch in diameter and 2.65 inchesin length has been used. The inner conductor had a diameterapproximately .08 of an inch. By using a powdered iron core withrelatively high permeability, the Q of the unit at 100 megacycles isapproximately 335. Used in a circuit as illustrated in Fig. 5, the tubeload reduced the Q to approximately 200. This is sufficiently high topermit high gain per stage and to provide good selectivity and imagerejection. Such a unit has an inductance of the order of .03 microhenryat the high frequency end which requires a tuning capacity ofapproximately 250 micromicrofarads. As the oscillator and variableintermediate frequency circuits are of lower frequency, the inductancevalues will be slightly higher and the transmission lines will,therefore, be longer.

When using the tuner in accordance with the invention for tuning aplurality of resonant circuits, as, for example, in a doublesuperheterodyne receiver as illustrated in Fig. 5, the various resonantcircuits can be aligned at the low frequency end of the band byadjusting the relative position of the cores in the transmission linesand at the high frequency end by the use of the integral trimmercapacitors. Referring to Fig. 1, it is apparent that the cores l2 areadjustably secured to the carriage I3 by the nuts 35. Therefore, thecircuits can be first aligned at the low frequency end by adjusting theposition of the cores I! with respect to the carriage l3 so that thevarious resonant circuits have the desired frequency relation. Then thecircuits can be tuned to the high frequency end of the band and alignedby adjusting the position of the plates 44 of the trimmer capacitors(Fig. 3). As the various tuning units will be of generally the sameconfiguration, the calibration of the individual units will followsubstantially the same characteristics so that the desired frequencyrelation will be substantially maintained throughout the entirefrequency band. As will be explained, the conductors of the transmissionline can be shaped as in Fig. 6 to provide a relatively straight line;frequency characteristic. It is readily apparent that. by. proper designof the conductors special frequency characteristicscan be obtained. Thefrequency characteristics of the tuning units also, depend, upon thepermeability of the material used in the core and, therefore, by usingmaterials of different permeability in various tuning units, specificdesired frequency characteristics can be obtained. For example, in thecircuit illustrated in Fig. the transmission lines in the three circuitscould be made the same length, and by using cores of higherpermeability,the inductance can be increased to provide the frequency relation in thethree circuits required.

Thecalibration-of the tuning units as disclosed aboveis generallysimilar to that of a variable condenser resulting in bunching of thechannelsat the higher frequency end. It has been found that amore nearlystraight line frequency characteristic can be obtained by changing theconfiguration of the conductors of the transmis- In Fig. 6 there isillustrated a modifled structure in which the. center conductor 90slants with respect to the outer conductor 9|, being positioned adjacentthe outer conductor at point 92. where it is connected thereto and beingsubstantially centrally located with respect to the outer conductor atthe open end 93. An iron core 94 can be generally similar to that in theprevious modifications except that a slanting slot 95 conforminggenerally to the slant of the center conductor Si! is required. In someapplications the use of a unit such as disc osed in Fig. 6' may bedesired to provide a more frequency distribution. For example, thisarrangement may in some instances facilitate tracking of variouscircuits which are ganged for operation of single control. It is obviousthat in the unit of Fig. 6, fixed, trimmer or center tapped capacitorscan be provided as an integral part of the unit in the same manner as inFigs. 3 and 4.

Extensive tests made using tuning, units in accordance with theinvention have been highly satisfactory. The units can be veryinexpensively constructed as the dimensions thereof are not critical.Using materials with maximum commercial tolerances for the inner andouter conductors, the variation in the inductance of the transmissionline is only plus or minus from nominal. This is sufficiently accuratethat the units can be fabricated Without electrical checking therebymaterially reducing the cost of the units. The provision of thecapacitors as an integral part of the tuning unit further decreases thecost and provides a high degree of uniformity in production not possiblein the construction of separate units.

use of a tuning capacity which isv correspondingly larger. fore, theeffect of the changing capacity of components due to warm-up, etc., ismuch less and the frequency drift caused thereby is correspondinglyless. the inductances and capacitors high gain and good selectivity.

Although I have described certain embodiuniform ments of my inventionit'is apparent that variousv changes and modifications can bemadetherein nected spaced coaxial conductors, a ferromagon saidtransmission line at the open end thereof, each of said plates beingelectrically connected to one of said conductors to provide a movablymounting one of said plates on said conductor to which it plate can bemoved tors being connected in series, a ferromagnetic capacitors connecmission line.

I circuit comprising a. transmission line including a pair of seriescon,-

means including a plurality of plates mounted on said transmission lineand electrically connected to said conductors to provide a pair ofcapacitors bridged across said transmission line, one of said platesbeing movable with respect to said other plates so that one of saidcapacitors is variable, common operating means for said inductancevarying means for simultaneously tuning said plurality of circuits, andadjustable means for connecting said inductance varying means to saidcommon operating means for aligning said circuits at the low frequencyend of said band, said variable capacitors being adapted to be used foraligning said circuits at the high frequency end of said band.

6. A resonant circuit comprising a tuning unit including a tunabletransmission line having a :pair of spaced conductors and aferromagnetic core movable in the space between said conductors forvarying the inductance thereof, and a capacitor bridged across saidtransmission line, said conductors being positioned with respect to eachother so that the movement of said core with respect to said conductorsproduces a change in the resonant frequency of said circuit which variessubstantially linearly with movement of said core.

'7. A tuning unit for use with a wave signal receiver comprising atransmission line including a center conductor and a cylindrical outerconductor coaxial therewith, said conductors bein substantiallycoextensive in length, means supporting said center conductor from saidouter conductor and electrically connecting said conductors at one endthere-of, and a ferromagnetic core movable in the space between saidconductors for varying the inductance of said serially connectedconductors, said core being insulated from said conductors and having aslot therein to clear said center conductor and said supporting meanswhen said core is moved with respect to said conductors.

8. A tuning unit for use with a wave signal receiver comprising atransmission line including an inner conductor and a cylindrical outerconductor, said inner conductor being connected at one end to one end ofsaid outer conductor and extending in substantially a straight line fromthe periphery of said outer conduct-or at said one end to the axis ofsaid outer conductor at the end thereof opposite to said one end, and aferromagnetic core movable in the space between said conductors andinsulated therefrom for varying the inductance of said seriallyconnected conductors.

9. A tuning unit for use with a wave signal receiver comprising atransmission line including an inner conductor and a cylindrical cuterconductor, said inner conductor being connected at one end to one end ofsaid outer conductor and extending in substantially a straight line fromthe periphery of said outer conductor at said one end to the axis ofsaid outer conductor at the end thereof opposite to said one end, and aferromagnetic core movable in the space between said conductors andinsulated therefrom for varying the inductance of said seriallyconnected conductors, said core having a slot therein to clear saidinner conductor when said core is moved with respect to saidconductors.

10. A wave signal receiver including a plurality of resonant circuitstunable to different frequencies having a predetermined frequencyrelation through a band of frequencies, tuner means for said receiverincluding a tuning unit in each of said circuits for tuning the same,each of said tuning units including a tunable transmission line having apair of spaced conductors and a magnetic core movable in the spacebetween said conductors for varying the inductance thereof, saidconductors being positioned with respect to each other so that themovement of said core with respect to said conductors produces a changein the resonant frequency of the associated circuit which variessubstantially linearly with movement of said core, and means forsimultaneously moving said cores with respect to said conductors, saidtuning units being so constructed that simultaneous movement of saidcores provides the inductance required in said circuits to substantiallymaintain said predetermined frequency relation through the desired bandof frequencies.

11. In a wave signal receiver including a plurality of resonant circuitstunable to frequencies having a predetermined frequency relation througha band of frequencies, a tuner comprising a plurality of tunabletransmission lines conncted in said circuit for tuning the same, 'eachof said lines including outer and inner spaced conductors and aferromagnetic core movable in the space between said conductors forvarying the inductance thereof, condenser means connected across saidtransmission lines including plates mounted on and electricallyconnected to said conductors, insulating frame means supporting saidouter conductors to form a unitary structure, and a movable carriagesupporting said cores for simultaneously moving said cores with respectto said conductors.

12. A tuning unit for use with a wave signal receiver comprising, atransmission line including a center conductor and a cylindrical outerconductor coaxial therewith, a core movable in the space between saidconductors for varying the electrical characteristics of the mediumseparating said conductors, a conducting member connected to saidconductors at one end thereof for electrically and mechanicallyinterconnecting the same, and a concentric capacitor connected acrosssaid transmission line at the end thereof opposite to said one end, saidcapacitor including plates individually connected electrically andmechanically to said conductors, said core being of such configurationto be msertable in said outer conductor at said one end thereof and toclear said inner conductor and said conducting member.

13. A tunable resonant circuit for use with a wave signal receivercomprising, a pair of spaced coaxial conductors, a concentric capacitorat one end of said conductors including plates individually secured tosaid conductors and electrically connected thereto, conducting meanselectrically interconnecting said coaxial conductors at points spacedfrom said capacitor, and a core movable in the space between saidconductors for varying the electrical characteristics of the mediumtherein, said core being of such configuration to be insertable in thespace between said conductors at the end thereof opposite to said oneend and to be spaced from said conductors and said conducting meansduring movement thereof.

14. A wave signal receiver including a plurality of resonant circuits, atuning unit in each circuit for tuning the same, each of said unitsincluding a transmission line having a center conductor and a coaxiallyspaced cylindrical outer conductor, conducting means at one end of saidtransmission line electrically interconnecting said conductors, aferromagnetic core movable in the space between said conductors forvarying the inductance thereof, said core being insulated from m n b i gj stab in a said outer conductor and being of such configuration toclear said center conductor and said conducting means during movement ofsaid core, and capacitor means secured to said transmission line at theend thereof opposite to said one end, said capacitor means including aplurality of annular plates of substantially the same diameter as saidouter conductor, each of said plates being connected to one of saidconductors to provide a plurality of capacitors bridged across saidtransmission line.

with a "wave signal a transmission line including and a cylindricalconductor means electrically interconnectingsaid conductors at one endof said transthe medium therein, said core being "of such configurationto be insertable in thespace between said conductors at said one endandto be'spaced from said conductors and said conducting means duringmovement ofsaid core and a capacitor, including a'pair of spacedcircular plates, secured to said transmission line at theend thereofopposite to said one end, said circular plates having substantially thesame outside diameter as said cylindrical conductor, 'one of said platesbeing connected at the center thereof to said center conductor and theother of said plates beingc'onn'ec'ted at'the edge thereof to saidcylindrical conductor to close said opposite end of said transmissionline, whereby said capacitor is electrically bridged across saidtransmission line, and with one of said platesb'eing adjustable in adirection longitudinally of the unit and relative to the other plate tovary the capacity of the capacitor.

17. A tuning unit comprising an outside openended cylindrical conductordefining substantially the outside dimensional limits in crosssection ofthe unit, an inside rod-like conductor within said outside conductor andlongitudinally thereof and secured at one end in an electrical andphysical connection to said outside conductor at one open end thereof,means substantially in said dimensional limits at the other open end ofsaid outside conductor supporting and centering the corresponding end ofthe inside conductor and providing in combination an electricalconnection at that end between saidinside and said outside conductorsand a capacitor, said means at saidother open end including a pluralityof plate means with one of said plate means in electrical connectionwith said center conductor and with another plate means operativelyconnected physically with said outer conductor and electricallyconnected thereto, with at least one plate direction generally otheropenend to toward and away from a d .7

the named plate vary the distance between means and to permitmove-v 12means, and a movable core within the cylindrical conductor ofsuchconfig-uration as tobe maintained out of contact with said insideconductor, with said core being insertable at said one end for movementto vary the permeability thereof.

receiver including in combination, a transmission line including acylindrical outer conductor, an inner conductor having a portionextending substantially coaxial with said outerconductor, said innerconductor having a projecting portion extending transversely from saidcoaxially extending portion and electrically connected to said outerconductor, and a core movable in the space between said conductors forvarying the electrical characteristics of the space therebetween, saidcore being insulated from said ccndu ctors'and having a slot therein toclearsaid coaxial and projecting portions of said inner conductor-"whensaid core is moved with respect to said conductors and past saidtransversely projecting portion.

19. A tuning unit tunable over a range of frequencies including incombination, longitudinally extending outer conductor means having aninner longitudinal cavity therein innerconductor means including arod-like conductingportion extending longitudinally within said cavityin said outer conductor means and a conducting arm portion extendingtransversely in the space mechanically interconnecting said rod-likeconducting portion and said outer conductormeans, and an elongated coreelement havindw crosssection proportioned tosubstantially conformto thecross-section of said cavity within said outer conductor means and beingslotted longitudinally thereof to permit movement of said coreelementpast said arm portion, said core element and said outer conductor meansbeing electrically insulated from each other and adjustable relative toeach other to change the electrical characteristics of the mediumseparating saidouter conductor means and said conducting portion tothereby adjust the resonant frequency of the tuning unit.

20. A tunable resonant circuit for use with a wave signal receiverincluding in combintion, first conducting means having a conductorportion forming the central conductor'of a coaxial transmission line,second conducting means having a portion extending transversely fromsaid central conductor portion at one end thereof and electricallyconnected to said cylindrical conductor portion to form a closedtransmission line, said first and second conducting means each having atthe end thereof opposite movable in the space between said coaxialconductor portions for varying the electrical characteristics of themedium therein, said "corebeing of such configuration to be insertable'in the space between said ment of said core.

21. A tunable resonant circuit'for use with a wave signal receiverincluding in combination,

first conducting means having a conductor. portion forming the centralconductor of a coaxial transmission line, second conducting means havinga conductor portion forming the outer cylindrical conductor of saidcoaxial transmission line, said first conducting means including aprojecting portion extending transversely from said central conductorportion at one end thereof and electrically connected to saidcylindrical conductor portion to form a closed transmission line, saidfirst and second conducting means having spaced conducting portions atthe end thereof opposite to said one end forming condenser meansconnected across said transmission line, at least a part of one of saidconducting portions being movable with respect to another one of saidconducting portions to change the capacity of said condenser means, andan elongated core movable in the space between said coaxial conductorportions for varying the electrical characteristics of the mediumtherein, said core being of such configuration to be insertable in thespace between said coaxial conductor portions and having a longitudinalslot therein to clear said transversely projecting portion and therebypermit movement of said core past said transversely projecting portion.

22. A tunable resonant circuit including first and second conductingmeans, said conducting means individually including conductor portionsforming a coaxial transmission line, one of said conducting meansincluding a projecting portion extending transversely between saidconductor portions and electrically interconnected to the other one ofsaid conducting means so that said transmission line is closed at oneend, an elongated ferromagnetic core movabl in the space between saidconductor portions for varying the inductance thereof, said core havinga longitudinal slot therein to permit movement of said core past saidtransversely projecting portion, said conducting means individuallyincluding conducting portions at the open end of said transmission line,said conducting respect to each other to form a plurality of capacitorsbridged across said transmission line, and means for movably mountingone of said conducting portions with respect to another one of saidconducting portions for varying the capacity of at least one of saidcapacitors.

23. A wave signal receiver including in combination a plurality ofresonant circuits having a predetermined frequency relation through aband of frequencies, a tuning unit in each circuit for tuning the same,each of said units ineluding first and second con-ducting meansindividually having conductor portions forming a center conductor and aspaced cylindrical outer conductor of a coaxial transmission line, oneof said conducting means of each unit including a projecting portionextending transversely between said conductor portions and electricallyinterconnected to the other one of said conducting means, an elongatedferromagnetic core movable in the space between said conductors of eachunit for varying the inductance thereof, said core having a longitudinalslot therein to permit movement of said core past said transverselyprojecting portion, said Conducting means indi vidually includingconducting portions with the conducting portions of each unit spacedwith respect to each otherto provide at least one capacitor bridgedacross the transmission line of the unit, one of said conductingportions of each unit being movable with respect to another one portionsbeing spaced with of said conducting portions to provide variation inthe capacity of one of said capacitors for aligning said circuits.

24. A device for tuning a high frequency circuit, comprising anelongated high permeability core member provided with a radial slotextending lengthwise of it, and an electrical conductor member havingends adapted to be connected in said circuit, said conductor having aportion extending from one of said ends into said slot and lengthwise ofthe inside of the core and having another portion extending along theoutside of the core lengthwise thereof, whereby to provide smallinductance for said circuit, and one of said members being movablerelative to the other to vary said, inductance.

25. A device for tuning a high frequency circuit, comprising a tubularmetal case, an elongated high permeability core disposed in the case andslidable lengthwise through an open end thereof, said core beingprovided with a radial slot extending lengthwise of it, and a metalconductor element extending into said slot adjacent said open end of thecase and then lengthwise of the inside of the core toward the oppositeend of the case, one end of said element engaging the case, and one endof the case and the free end of said element being adapted to beconnected in said circuit, whereby an inductive circuit is formedthrough said element and case which can be varied by sliding the core orcase lengthwise relative to the other.

26. A device for tuning a high frequency circuit, comprising anelongated high permeability core member provided with a radial slotextending lengthwise of it, and an electrical conductor member havingends adapted to be connected in said circuit, said conductor havingsubstantially parallel straight portions extending lengthwise of thecore member, one of said portions extending from one of said ends intosaid slot and lengthwise of the inside of the core member, and the otherof said portions extending lengthwise of the outside of the core member,whereby to provide small inductance for saidcircuit, one of said membersbeing movable relative to the other to vary said inductance.

27. A device for tuning a high frequency circuit, comprising anelongated high permeability core member provided with a radial slotextending lengthwise thereof, and a conducting member having endsadapted to be connected in said circuit, said conducting member having afirst portion extending into said slot and lengthwise of the inside ofsaid core and having another portion extending along the outside of saidcore, whereby to provide small inductance for the circuit, and one ofsaid members being movable lengthwise relative to the other to vary theamount of said first portion of said conducting member inside the corein order to vary said inductance.

28. A variable inductance for very high frequency circuits including amovable elongated core of low permeability, a first conducting elementof low inductance, a second conducting element of considerably higherinductance, means connecting said elements in series in additive sense,one of said elements being an outer element and the other element beingan inner element located inside said outer element, said core having across section of such dimensions to be movable within said outer elementand including a cavity extending lengthwise thereof to ac- "crimmiiatesaid inner --element" *to' therebypro 'du'ce induotance 21arzanf'z'onxsin both elements.

GUS -W. WALLIN.

REFERENCES CITED 'The following references areof record in' the fileofthis patent or the original patent:

UNITED STATES PATENTS Number Name .Date

1,955,093 Roosenstein '.Ap'r. 11,1934 2,097,519 =Gabrie1 Nov, ;2,. 193.7"2,:I53;205 Park Apr. 4, 1939 2,157,855 :Kook a. Mays 1939 2,286,428'M'ehIer Y 1 J1Jne .16, 7 1942 16 Number Name Date "2,402948 Carlson.Ju1y'2, 1946 2,408,895 Turner Oct. 8, 1946 2,497,662 Dressel i- Feb.14, 1950 2,518,938 Polydoroff -Aug. 15, 1950 OTHER REFERENCES Reprintfrom Proceedings of the National Electronics Conference, volume 2, 1946,paper on V-H-F Tuner Design by Gus Wallin and C.- W. Dymond. Copy inthis application file attached 131 afiidayit.

Article, Coaxial Coils for F. M. Permeability Tuners by W. J.Polydoroff, published in Radio January 194?, pages 9, 10, 31 and 32.

